California's kelp forests have shrunk by millions of square meters
Kelp, which supports the marine ecosystem, has been severely impacted by warming oceans
By Ilena Peng
California has lost over 99% of its kelp forests in just over a decade, according to research from a team of researchers at the University of California.
Using satellite imagery, the researchers detected over 3.5 million square meters of kelp in 2008 along the coastline bordering Mendocino and Sonoma counties. By 2019, that number dropped to fewer than 11,000 square meters.
California’s kelp forests, sometimes referred to as the Sequoias of the Sea, are the backbone of an entire marine ecosystem. The waving fronds sustain small critters like snails, crabs, sea urchins and abalone, which in turn feed otters and other larger animals. But as the climate continues to warm in recent years, the forest has started to disappear.
"Imagine you were walking in the forest on your favorite trail, surrounded by tall beautiful trees, singing birds, flowers, animals, etc," said Meredith McPherson, the paper’s lead author and a postdoctoral researcher at University of Massachusetts Boston.
"And then imagine that suddenly one day you went back for a hike and that forests had disappeared. Completely replaced by nothing other than dirt and maybe some weeds. Imagine that it stretches for hundreds and hundreds of miles. That is what has happened to the kelp forests in northern California."
Westport
Fort Bragg
Mendocino
MENDOCINO COUNTY
Anchor Bay
SONOMA
COUNTY
Stewarts Point
Fort Ross
25 km
Westport
Fort Bragg
Mendocino
MENDOCINO COUNTY
Anchor Bay
SONOMA
COUNTY
Stewarts Point
Fort Ross
25 km
Westport
Fort Bragg
MENDOCINO
COUNTY
Mendocino
Anchor Bay
SONOMA
COUNTY
Fort Ross
25 km
Warming waters also facilitated the forests’ decline by creating favorable conditions for purple sea urchins, who feed on kelp forests. Urchins are “survivors” and can exist for a long time in starvation mode. Their populations have been growing unchecked since the sea star population that feeds on urchins has dropped as a result of sea star wasting disease.
McPherson said some efforts to restore the forest have included removing or limiting urchin populations. Some businesses have even begun harvesting the sea urchins for uni, often served at Japanese sushi restaurants. There have also been efforts to plant kelp to generate new forests, surround existing kelp patches with urchin proof barriers and create a kelp spore bank to preserve the organism’s gene pool, McPherson said.
The kelp forest could be naturally restored as well, if ocean conditions shift to become more favorable for kelp or if a disease kills off purple sea urchins. But without those, urchin barrens — vast areas covered only by urchins — can persist for decades, as has occurred in some areas of Norway.
As the kelp forest faces losses, so do the creatures and cultures that depend on it. Red abalone, which eats kelp and other algae, no longer has a sufficient food source. Their populations have dropped so much as a result that recreational divers are not allowed to fish for red abalone until at least 2026. If the recreational red abalone fishery were to close permanently, it would amount to an economically and culturally significant loss for Northern California counties.
But even if what happened underwater had no impact on us at all, the death of a kelp forest would still send shockwaves through the marine ecosystem.
"The value of these ecosystems is hard to quantify, but even if humans didn't care or depend on it, the loss of biodiversity, habitat structure, carbon/nutrient cycling is huge," McPherson said.
Data and code are available on GitHub.